This project will study the temporal relation between the anatomical appearance of synaptic connections in the nervous system and when these connections first effect behavior. At present, results related to this problem have included only general descriptions of behavioral and synaptic development. One reason for this is that with the techniques presently available the cell bodies of origin of the synaptic knobs being studied cannot be identified. In this project methods will be applied to the developing nervous system to remedy this difficulty which are already being used in the adult nervous system. These include light microscopic techniques for staining degenerating axons and synaptic knobs and electron microscopic criteria for recognizing the degeneration of these structures. These methods, along with other presently available techniques for revealing synaptic knobs, will first be used to trace the normal development of synaptic knobs from several sources in the spinal cord and relate their appearance to the time that these knobs first effect behavioral response development. This information will then be used to see if it is related to the sparing of function observed after lesions in young animals. The hypothesis that sparing of function is dependent on an actual synaptic rearrangement in the developing nervous system will also be tested.